Transmit diversity with formed beams in a wireless communications system using a common pilot channel

ABSTRACT

A method and apparatus are provided that allows beamforming to be used on a user-specific signal together with a sector-wide pilot signal in a communication system, such as a CDMA system. In one embodiment, the invention includes transmitting a pilot signal with a wide beamwidth to a remote terminal from a first array, transmitting a first traffic signal with a narrow beamwidth directed to the remote terminal from the first array, and transmitting a second diversity traffic signal with a second narrow beamwidth directed to the remote terminal from a second array. In some examples, the invention may also include transmitting a second pilot signal from the second antenna array.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is continuation of prior application Ser. No.10/186,986, filed Jun. 28, 2002 now U.S. Pat. No. 7,206,554, with thesame title, the priority of which is hereby claimed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of digital radiosignal communications. More particularly, the invention relates to usingtransmit diversity with user-specific transmission parameters togetherwith a common pilot signal.

2. Description of the Related Art

Many wireless data communication systems use training information orpilot signals that the receiving terminal uses to demodulate receivedtraffic, control, overhead or other signals. One such example is thepilot signal transmitted by a base station in a CDMA (code divisionmultiple access) communications system. Typically a single common pilotsignal is transmitted to all remote or subscriber terminals in the basestation's coverage area. The coverage area of the base station istypically referred to as a sector. Any signals transmitted to anyparticular user terminal can then be resolved with the help of thetiming and phase information in the common pilot signal.

The pilot signal is particularly effective when the signal propagationpath for both the pilot and the user-specific signal is the same. In aCDMA system in which the pilot and user-specific signal are sent overthe same frequency band from the same antennas but with differentscrambling codes, the pilot signal is very effective. However, anydifference between signals makes the pilot signal more difficult to useor, in other words, it makes the user-specific signal more difficult todemodulate. If, for example, the user-specific signal is spatiallydirected toward the remote terminal and the pilot signal is a commonsector-wide signal, then the two signals can traverse a different signalpropagation path. This will cause the two signals, as received by theremote terminal, to differ.

The propagation channel of the pilot signal and the propagation channelof the traffic channel will differ whenever they are transmitted withbeams of different width and shape. The user terminal typically uses thepilot signal to estimate a channel that then is used in the process ofdemodulating and detecting the symbols transmitted on the trafficchannel. The difference in the propagation channel of the pilot signaland the traffic channel therefore reduces the accuracy of the channelestimate. To compensate, each user can be provided with a user-specificpilot signal but this greatly increases the amount of traffic on thenetwork.

BRIEF SUMMARY OF THE INVENTION

A method and apparatus are provided that allows beamforming to be usedon a user-specific signal together with a sector-wide pilot signal in acommunication system, such as a CDMA system. In one embodiment, theinvention includes transmitting a pilot signal with a wide beamwidth toa remote terminal from a first array, transmitting a first trafficsignal with a narrow beamwidth directed to the remote terminal from thefirst array, and transmitting a second diversity traffic signal with asecond narrow beamwidth directed to the remote terminal from a secondarray. In some examples, the invention may also include transmitting asecond pilot signal from the second antenna array.

Other features of the present invention will be apparent from theaccompanying drawings and from the detailed description that follows.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings in which likereference numerals refer to similar elements and in which:

FIG. 1 is a flow chart showing one embodiment of the present invention;

FIG. 2 is a flow chart showing a process for optimizing transmissionparameters for use in one embodiment of the present invention;

FIG. 3 is a simplified block diagram of a base station on which anembodiment of the invention can be implemented; and;

FIG. 4 is a block diagram of a remote terminal on which an embodiment ofthe invention can be implemented.

DETAILED DESCRIPTION OF THE INVENTION Introduction

This invention allows beamforming to be used on a user-specific signaltogether with a sector-wide pilot signal in a communication system, suchas a CDMA system. Only one pilot signal is required in the sector,although two can be used if the transmit diversity scheme requires. Whenbeamforming is used on, for example, a traffic channel together with asector-wide pilot, the difference in angular spread in the twopropagation channels causes a mismatch in how the traffic channel andthe pilot signal are received.

The difficulties caused by this mismatch can be alleviated by combiningbeamforming on the traffic channel with a sector wide pilot and atransmit diversity scheme. Adding transmit diversity adds a level ofdiversity into the channel mismatch. That is, the impairment due to thephase error (or other channel mismatch), is reduced by the fact thatthere are two different channels from the base station to the userterminal. The likelihood that both will have a large mismatch at thesame time is less than the likelihood that any one of the channels willhave a large mismatch. The robustness of the channel is significantlyenhanced in a receiver that is designed to receive the particular typeof diversity signals.

The present invention is described in the context of wireless basestations for air interfaces that allow beam forming, but it is not solimited. It is particularly applicable to wireless systems in which apilot signal typically is shared among multiple users at the same time,as is commonly required in standards for CDMA (code division multipleaccess) systems. Current examples of such wireless systems are WCDMA(wideband CDMA), cdma2000, IS-95 (interim standard 95 of theTelecommunications Industry Association). The present invention may alsobe applied to some TDMA (time division multiple access) systems such asthe downlink of HDR (high data rate for CDMA) and GSM (Global System forMobile Communications).

Process Flow

FIG. 1 shows a process flow diagram for optimizing transmit parametersin accordance with the present invention. This process is described inthe context of a base station (BS), in a network that includes many basestations, sending a pilot signal to any subscriber stations or remoteuser terminals that may be within range of the base station.

The base station may be equipped with any of a variety of differentantenna configurations. For example, the base station may use two ormore spatially separated antenna arrays 4-1, 4-2, 4-3 each with closelyspaced antenna elements. The antenna elements can be spaced on the orderof one half the wavelength of a typical signal carrier wave, while thearrays are spaced apart by at least a distance of several carrierwavelengths. Antenna arrays with similar spacing between elements canalso be used with different polarization. In other words, two arrays ofantennas differentiated either by their spatial location (e.g. 10-20lambda or more apart) or by having different polarization (e.g. +45 and−45 degree polarization respectively) can be applied. Other types ofantenna arrays may also be used.

The BS, or any radio operating in accordance with the present invention,transmits a pilot signal with a wide beamwidth 305 to any remote radiosin range, for use as a phase reference to demodulate a traffic channelsignal. The pilot channel can be transmitted across an entire sector ofthe base station or any subsector. The pilot signal can be transmittedon one or two sector-wide beams. The base station also transmits a firsttraffic signal with a narrow beamwidth 307 and transmits a seconddiversity traffic signal with a second narrow beamwidth 309.

The narrow beamwidths can be selected using signal processing resources31, 33 of the base station specifically to provide diversity receptionat a particular remote radio. Accordingly they are transmitted withdifferent signal transmission parameters. The diversity signals, asmentioned above can be transmitted in accordance with any desireddiversity scheme. According to some standards for transmit diversity,the base station will also transmit a second pilot signal from thesecond antenna array 311. These beams are typically all transmittedsimultaneously, however, the particular timing of the transmissions willdepend upon the particular diversity mode employed.

In one embodiment, the two user-specific narrow beamwidth signals aretransmitted using a transmit diversity scheme like the closed looptransmit diversity scheme in WCDMA. In this case, two slightly differentpilot signals are transmitted, one on a sector wide beam from the firstarray and one on a sector wide beam from the second array. Using thesepilot signals the user terminal estimates the channel to each array andtells the base station how it should change the phase and possibly theamplitude of the traffic signals transmitted from each of the arrays sothat the signals combine as coherently as possible. Since the trafficsignal now arrives on two different beams with different channelmismatch, the user terminal benefits from this diversity in the channelmismatch, as mentioned above.

In another embodiment, the two user-specific narrow beamwidth signalsare transmitted using an open loop transmit diversity scheme like, forexample, either of the space-time block coding schemes in cdma2000 orWCDMA. In this embodiment, each part of the space-time block codingsignal is transmitted over one of the beams. The user terminal thencombines the signal in its receiver according to the space-time blockcoding algorithm, as detailed in the respective standards. In thisembodiment, the user also receives the signal on two different beamswith different channel mismatch. Again providing a performanceimprovement due to diversity.

Using conventional receivers and signal processors 68 and applying theapproaches described above, the conventional receiver's tolerance toangular spread is significantly increased. This occurs with closed loopand open loop transmit diversity schemes that follow the standards forwhich the receiver is designed. In other words, the same BER (bit errorrate) can be achieved with a significantly larger angular spread thanwithout using the diversity transmission mode. This effect is not due tomultipath, fading or other problems which diversity transmission istypically deployed to solve. The performance increase comes because thediversity transmission allows the receiver to overcome the phasemismatch between a directed traffic or other user-specific channel and acommon pilot channel. As a result, the same channel quality can beobtained with all the benefits of directing narrow beams specifically tothe intended user.

Optimizing Transmit Parameters

To further enhance reception by the remote terminal, the transmitparameters can be optimized. This can be done in a variety of differentways well-known in the art. An alternative useful and novel approach isdescribed below with respect to FIG. 2. This process is described in thecontext of a base station (BS), in a network that includes many basestations, sending a BCH burst to any subscriber stations or remote userterminals that may be within range of the base station.

First a BS, or any radio operating in accordance with the presentinvention receives signals from a remote radio 105, for example thesubscriber terminal shown in FIG. 6. Based on these received signals theBS can derive estimates of the channel on which the signals werereceived 107. From the estimate of the receive channel, a model of theexpected transmit channel can be derived 109 and from that a model ofthe transmit weights 111 that can be used to transmit a user-specificsignal back to the remote radio over the model of the transmit channel.Alternatively, any other set of parameters can be used instead ofweights depending on the design of the system. Some systems may usesignatures, vectors, or other types of parameters to control thetransmission of a signal by a set of antenna elements.

The weights or other parameters are then optimized before use by atransmit power criterion 113. This can be done by developing a model ofthe expected transmit channel 115 and applying constraints on theestimated quality of the resulting transmitted signal 117. There are avariety of different constraints as described below. The optimizationcan be used to maximize the received power of the remote terminal ascompared to the transmitted power. Having optimized the transmissionparameters, they can be used to transmit a communications signal to theremote terminal 119. For example, the signal can be transmitted to theremote radio by applying a derived set of transmit weights to theelements of a transmit antenna array.

Outer Loop Target SINR Optimization

Considering the example of FIG. 2, above in more detail, thetransmission parameters can be optimized in one embodiment of theinvention using an outer loop target SINR optimization. In thisembodiment, the downlink transmission weights are selected based onestimates of the downlink performance of the selected weights. Theestimates are formed using models of the downlink channel derived fromthe uplink signals. The model can be an estimate of a downlink spatialcovariance matrix formed from a corresponding uplink spatial covariancematrix. The performance of the downlink weights can be estimated usingthe downlink channel model by estimating what outer loop SINR targetwould be required at the mobile in order to meet some specified outagerequirement.

The outage requirement can be formulated in terms of how often theuncoded or coded BER or FER can be below some threshold. The outagerequirement can also be formulated as how often the mismatch in phasebetween the traffic channel and the sector wide pilot can be above acertain level. The downlink weights giving the lowest estimated outerloop SINR target are then selected by solving an optimization problem,minimizing the outer loop SINR target.

The outer loop SINR target optimization approach can be applied to theexample of FIG. 2 in many different ways. In one embodiment of theinvention, a base station receives signals on an uplink channel from aremote terminal and estimates receive spatial signatures. The receivespatial signature can either be used to estimate transmit spatialsignatures or to estimate transmit spatial covariance matrix. Transmitspatial signatures and transmit spatial covariance matrices can beestimated in a variety of different ways well-known in the art. Thetransmit signatures or matrices can be a set of transmit signatures ormatrices derived on a tap-by-tap basis.

The transmit values can then be optimized using a model of the transmitor downlink channel. A suitable model can be formed as h=R^{H/2}v, wherev is a column vector with M complex Gaussian random elements, M beingthe number of transmit antennas, R^{H/2} being the Hermitian of theCholesky factorization of the estimated transmit covariance matrix and hbeing a realization of a transmit spatial signature. Differentrealizations of the transmit spatial signature can be generated bygenerating new random vectors v. If sets of signatures or matrices areused, this model can be applied to generate separate estimates of thetransmit spatial signatures for different taps in a transmitspatio-temporal channel model.

Using this, or another model, transmit weights can be found that resultin the lowest outer loop SINR target such that an outage requirement ismet. Several different outage requirements can be used or outagerequirements can be combined. One example is that the BER must be lessthan x percent at least y percent of the time. Another example is thatthe FER must be less than x percent at least y percent of the time. Athird example is that the phase error of the user-specific signalcompared to the phase of a pilot signal transmitted using a differentweight must be less than x degrees at least y percent of the time. Theselection of x and y will depend upon the particular configuration andrequirements of a specific implementation.

Applying the outage requirement allows transmit weights to be foundusing well-known algorithms for non-linear constrained optimization.Alternatively, the solution of the problem can be simplified byselecting from a predetermined family of weights. Each set of weights orweight vector in the family would be determined to produce a beam thatgives a maximum gain, computed as a weighted average over some angularregion, while meeting a constraint on the maximum deviation in the phaseof the beam from the beam used by the sector wide pilot over the same(or different) angular region.

Stated another way, each weight vector in the family of weight vectorsis parameterized by one or more real numbers. For example, each weightgenerates a beam of a different beamwidth. Each weight vector generatesa beam that has a constraint on the phase error of the generated beam ascompared to the phase error of the beam of, for example a common pilotsignal. The phase error constraint can also be a constraint on themaximum phase error as compared to the beam of the pilot signal for anrange of angles of arrival. Each weight vector also maximizes a functionof the gain over a range of angles of arrival. The particular parametersand constraints to be used in generating the predetermined family ofweight vectors will depend on the particular application.

Power Optimization Under a Phase Error Constraint

As an alternative to the outer loop target SINR optimization, in anotherembodiment, the parameters can be optimized by selecting the downlinktransmission weights as the weights that optimize the delivered powergiven a constraint on the phase error, and on the total transmittedpower.

The delivered power can be estimated using any of the downlink channelestimates described above. The constraint on the phase error can be aconstraint on the RMS (root mean square) phase error, the x:thpercentile of the phase error, where x is selected for a particularimplementation, or some other some other convenient form. Alternatively,instead of a phase error constraint, a constraint on the differencebetween the phasors of the pilot channel complex gain or channel and thetraffic channel complex gain or channel, or some other convenientfunction of the two channels can be used.

The power optimization approach can be applied to the example of FIG. 2in many different ways. In one embodiment, a base station derivestransmit spatial signatures or transmit spatial covariance matrices asdescribed above and a similar model of the downlink channel is derived.

The optimization problem in the present embodiment is to find a transmitweight vector that results in the maximum average delivered power, givena fixed transmit power, such that an outage requirement is met. Theoutage requirement can take many different forms. One such form is thatthe phase error of the user specific signal as compared to the phase ofa pilot signal transmitted using a different weight must be less than xdegrees at least y percent of the time. The transmit weight vector canbe found by using constrained optimization algorithms.

As with the example above, the solution of the optimization problem canbe simplified using a predetermined set of weight vectors from which toselect. The set of transmit weights can be parameterized by one or morereal numbers in the same manner as described above.

Base Station Structure

In one embodiment as discussed above, the present invention isimplemented in an SDMA (Spatial Division Multiple Access) radio datacommunications system. In such a spatial division system, each terminalis associated with a set of spatial parameters that relate to the radiocommunications channel between, for example, the base station and a userterminal. The spatial parameters comprise a spatial signature for eachterminal. Using the spatial signature and arrayed antennas, the RFenergy from the base station can be more precisely directed at a singleuser terminal, reducing interference with and lowering the noisethreshold for other user terminals. Conversely, data received fromseveral different user terminals at the same time can be resolved atlower receive energy levels. With spatial division antennas at the userterminals, the RF energy required for communications can be even less.The benefits are even greater for subscribers that are spatiallyseparated from one another. The spatial signatures can include suchthings as the spatial location of the transmitters, thedirections-of-arrival (DOAs), times-of-arrival (TOAs) and the distancefrom the base station.

Estimates of parameters such as signal power levels, DOAs, and TOAs canbe determined using known training sequences placed in digital datastreams for the purpose of channel equalization in conjunction withsensor (antenna) array information. This information is then used tocalculate appropriate weights for spatial demultiplexers, multiplexers,and combiners. Techniques well known in the art, can be used to exploitthe properties of the training sequences in determining spatialparameters. Further details regarding the use of spatial division andSDMA systems are described, for example, in U.S. Pat. No. 5,828,658,issued Oct. 27, 1998 to Ottersten et al. and U.S. Pat. No. 5,642,353,issued Jun. 24, 1997 to Roy, Ill. et al.

(SDMA) technology can be combined with other multiple access systems,such as time division multiple access (TDMA), frequency divisionmultiple access (FDMA) and code division multiple access (CDMA).Multiple access can be combined with frequency division duplexing (FDD)or time division duplexing (TDD).

FIG. 2 shows an example of a base station of a wireless communicationssystem or network suitable for implementing the present invention. Thebase station uses SDMA technology which can be combined with othermultiple access systems, such as time division multiple access (TDMA),frequency division multiple access (FDMA) and code division multipleaccess (CDMA). Multiple access can be combined with frequency divisionduplexing (FDD) or time division duplexing (TDD). The system or networkincludes a number of subscriber stations, also referred to as remoteterminals or user terminals, such as that shown in FIG. 3. The basestation may be connected to a wide area network (WAN) through its hostDSP 31 for providing any required data services and connections externalto the immediate wireless system.

To support spatial diversity, a plurality of antennas 3 is used to forman antenna array 4, for example four antennas, although other numbers ofantennas may be selected. Each antenna is an element of a four-elementarray 4. And a plurality of arrays are provided 4-1, 4-2, 4-3. Theantenna elements may have a spacing of from one-quarter to fourwavelengths of a typical carrier frequency while the arrays may beseparated by ten or twenty wavelengths. The best spacing for spatialdiversity will depend upon the particular frequencies involved, thephysical installation and other aspects of the system. In manyapplications, the spacing between antenna elements of each array can beless than two wavelengths of the received signal. The spacing betweenantenna arrays can be more than two wavelengths of the received signal.In general, the spacing between elements in an array is selected tominimize grating lobes when transmissions from each element arecoherently combined. In an alternative approach, the arrays are spacedapart so as to form a uniform array of elements. The distance betweennearest elements in different arrays is the same as the spacing betweenelements within an array. As mentioned above, it is also possible foreach array to have only a single element.

A set of spatial multiplexing weights for each subscriber station areapplied to the respective modulated signals to produce spatiallymultiplexed signals to be transmitted by the bank of four antennas. Thehost DSP 31 produces and maintains spatial signatures for eachsubscriber station for each conventional channel and calculates spatialmultiplexing and demultiplexing weights using received signalmeasurements. In this manner, the signals from the current activesubscriber stations, some of which may be active on the sameconventional channel, are separated and interference and noisesuppressed. When communicating from the base station to the subscriberstations, an optimized multi-lobe antenna radiation pattern tailored tothe current active subscriber station connections and interferencesituation is created. The channels used may be partitioned in anymanner. In one embodiment the channels used may be partitioned asdefined in the GSM (Global System for Mobile Communications) airinterface, or any other time division air interface protocol, such asDigital Cellular, PCS (Personal Communication System), PHS (PersonalHandyphone System) or WLL (Wireless Local Loop). Alternatively,continuous analog or CDMA channels can be used.

The outputs of the antennas are connected to a duplexer switch 7, whichin a TDD embodiment, may be a time switch. Two possible implementationsof the duplexer switch are as a frequency duplexer in a frequencydivision duplex (FDD) system, and as a time switch in a time divisionduplex (TDD) system. When receiving, the antenna outputs are connectedvia the duplexer switch to a receiver 5, and are converted down inanalog by RF receiver (“RX”) modules 5 from the carrier frequency to anFM intermediate frequency (“IF”). This signal then is digitized(sampled) by analog to digital converters (“ADCs”) 9. Finaldown-converting to baseband is carried out digitally. Digital filterscan be used to implement the down-converting and the digital filtering,the latter using finite impulse response (FIR) filtering techniques.This is shown as block 13. The invention can be adapted to suit a widevariety of RF and IF carrier frequencies and bands.

There are, in the example of GSM, eight down-converted outputs from eachantenna's digital filter 13, one per receive timeslot. The particularnumber of timeslots can be varied to suit network needs. While GSM useseight uplink and eight downlink timeslots for each TDMA frame, desirableresults can also be achieved with any number of TDMA timeslots for theuplink and downlink in each frame. For each of the eight receivetimeslots, the four down-converted outputs from the four antennas arefed to a digital signal processor (DSP) 31 an ASIC (Application SpecificIntegrated Circuit) or FPGA (Field Programmable Gate Array) (hereinafter“timeslot processor”) for further processing, including calibration,according to one aspect of this invention. For TDMA signals, eightMotorola DSP56300 Family DSPs can be used as timeslot processors, oneper receive timeslot. The timeslot processors 17 monitor the receivedsignal power and estimate the frequency offset and time alignment. Theyalso determine smart antenna weights for each antenna element. These areused in the SDMA scheme to determine a signal from a particular remoteuser and to demodulate the determined signal. In a WCDMA system, thechannels may be separated using codes in an FPGA and then furtherprocessed separately perhaps using separate DSPs for different users.Instead of being timeslot processors the processors are channelprocessors.

The output of the timeslot processors 17 is demodulated burst data foreach of the eight receive timeslots. This data is sent to the host DSPprocessor 31 whose main function is to control all elements of thesystem and interface with the higher level processing, which is theprocessing which deals with what signals are required for communicationsin all the different control and service communication channels definedin the system's communication protocol. The host DSP 31 can be aMotorola DSP56300 Family DSP. In addition, timeslot processors send thedetermined receive weights for each user terminal to the host DSP 31.The host DSP 31 maintains state and timing information, receives uplinkburst data from the timeslot processors 17, and programs the timeslotprocessors 17. In addition it decrypts, descrambles, checks errorcorrecting code, and deconstructs bursts of the uplink signals, thenformats the uplink signals to be sent for higher level processing inother parts of the base station.

Furthermore DSP 31 may include a memory element to store data,instructions, or hopping functions or sequences. Alternatively, the basestation may have a separate memory element or have access to anauxiliary memory element. With respect to the other parts of the basestation it formats service data and traffic data for further higherprocessing in the base station, receives downlink messages and trafficdata from the other parts of the base station, processes the downlinkbursts and formats and sends the downlink bursts to a transmitcontroller/modulator, shown as 37. The host DSP also manages programmingof other components of the base station including the transmitcontroller/modulator 37 and the RF timing controller shown as 33. The RFcontroller 33 reads and transmits power monitoring and control values,controls the duplexer 7 and receives timing parameters and othersettings for each burst from the host DSP 31.

The transmit controller/modulator 37, receives transmit data from thehost DSP 31. The transmit controller uses this data to produce analog IFoutputs which are sent to the RF transmitter (TX) modules 39.Specifically, the received data bits are converted into a complexmodulated signal, up-converted to an IF frequency, sampled, multipliedby transmit weights obtained from host DSP 31, and converted via digitalto analog converters (“DACs”) which are part of transmitcontroller/modulator 37 to analog transmit waveforms. The analogwaveforms are sent to the transmit modules 39. The transmit modules 39up-convert the signals to the transmission frequency and amplify thesignals. The amplified transmission signal outputs are sent to antennas3 via the duplexer/time switch 7. In a CDMA system, the signals may alsobe spread and scrambled using appropriate codes.

User Terminal Structure

FIG. 3 depicts an example component arrangement in a remote terminalthat provides data or voice communication. The remote terminal's antenna45 is connected to a duplexer 46 to permit the antenna 45 to be used forboth transmission and reception. The antenna can be omni-directional ordirectional. For optimal performance, the antenna can be made up ofmultiple elements and employ spatial processing as discussed above forthe base station. In an alternate embodiment, separate receive andtransmit antennas are used eliminating the need for the duplexer 46. Inanother alternate embodiment, where time division duplexing is used, atransmit/receive (TR) switch can be used instead of a duplexer as iswell known in the art. The duplexer output 47 serves as input to areceiver 48. The receiver 48 produces a down-converted signal 49, whichis the input to a demodulator 51. A demodulated received sound or voicesignal 67 is input to a speaker 66.

The remote terminal has a corresponding transmit chain in which data orvoice to be transmitted is modulated in a modulator 57. The modulatedsignal to be transmitted 59, output by the modulator 57, is up-convertedand amplified by a transmitter 60, producing a transmitter output signal61. The transmitter output 61 is then input to the duplexer 46 fortransmission by the antenna 45.

The demodulated received data 52 is supplied to a remote terminalcentral processing unit 68 (CPU) as is received data before demodulation50. The remote terminal CPU 68 can be implemented with a standard DSP(digital signal processor) device such as a Motorola series 56300 FamilyDSP. This DSP can also perform the functions of the demodulator 51 andthe modulator 57. The remote terminal CPU 68 controls the receiverthrough line 63, the transmitter through line 62, the demodulatorthrough line 52 and the modulator through line 58. It also communicateswith a keyboard 53 through line 54 and a display 56 through line 55. Amicrophone 64 and speaker 66 are connected through the modulator 57 andthe demodulator 51 through lines 65 and 67, respectively for a voicecommunications remote terminal. In another embodiment, the microphoneand speaker are also in direct communication with the CPU to providevoice or data communications. Furthermore remote terminal CPU 68 mayalso include a memory element to store data, instructions, and hoppingfunctions or sequences. Alternatively, the remote terminal may have aseparate memory element or have access to an auxiliary memory element.

In one embodiment, the speaker 66, and the microphone 64 are replaced oraugmented by digital interfaces well-known in the art that allow data tobe transmitted to and from an external data processing device (forexample, a computer). In one embodiment, the remote terminal's CPU iscoupled to a standard digital interface such as a PCMCIA interface to anexternal computer and the display, keyboard, microphone and speaker area part of the external computer. The remote terminal's CPU 68communicates with these components through the digital interface and theexternal computer's controller. For data only communications, themicrophone and speaker can be deleted. For voice only communications,the keyboard and display can be deleted.

General Matters

In the description above, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout some of these specific details. In other instances, well-knowncircuits, structures, devices, and techniques have been shown in blockdiagram form or without detail in order not to obscure the understandingof this description.

The present invention includes various steps. The steps of the presentinvention may be performed by hardware components, such as those shownin FIGS. 2 and 3, or may be embodied in machine-executable instructions,which may be used to cause a general-purpose or special-purposeprocessor or logic circuits programmed with the instructions to performthe steps. Alternatively, the steps may be performed by a combination ofhardware and software. The steps have been described as being performedby either the base station or the user terminal. However, many of thesteps described as being performed by the base station may be performedby the user terminal and vice versa. Furthermore, the invention isequally applicable to systems in which terminals communicate with eachother without either one being designated as a base station, a userterminal, a remote terminal or a subscriber station. Thus, the presentinvention is equally applicable and useful in a peer-to-peer wirelessnetwork of communications devices using spatial processing. Thesedevices may be cellular phones, PDAs, laptop computers, or any otherwireless devices. Generally, since both the base stations and theterminals use radio waves, these communications devices of wirelesscommunications networks may be generally referred to as radios.

In portions of the description above, only the base station is describedas performing spatial processing using adaptive antenna arrays. However,the user terminals can also contain antenna arrays, and can also performspatial processing both on receiving and transmitting (uplink anddownlink) within the scope of the present invention.

Furthermore, in portions of the description above, certain functionsperformed by a base station could be coordinated across the network, tobe performed cooperatively with a number of base stations. For example,each base station antenna array could be a part of a different basestation. The base station's could share processing and transceivingfunctions. Alternatively, a central base station controller couldperform many of the functions described above and use the antenna arraysof one or more base stations to transmit and receive signals.

The present invention may be provided as a computer program product,which may include a machine-readable medium having stored thereoninstructions, which may be used to program a computer (or otherelectronic devices) to perform a process according to the presentinvention. The machine-readable medium may include, but is not limitedto, floppy diskettes, optical disks, CD-ROMs, and magneto-optical disks,ROMs, RAMs, EPROMs, EEPROMs, magnet or optical cards, flash memory, orother type of media/machine-readable medium suitable for storingelectronic instructions. Moreover, the present invention may also bedownloaded as a computer program product, wherein the program may betransferred from a remote computer to a requesting computer by way ofdata signals embodied in a carrier wave or other propagation medium viaa communication link (e.g., a modem or network connection).

Many of the methods are described in their most basic form, but stepscan be added to or deleted from any of the methods and information canbe added or subtracted from any of the described messages withoutdeparting from the basic scope of the present invention. It will beapparent to those skilled in the art that many further modifications andadaptations can be made. The particular embodiments are not provided tolimit the invention but to illustrate it. The scope of the presentinvention is not to be determined by the specific examples providedabove but only by the claims below.

It should also be appreciated that reference throughout thisspecification to “one embodiment” or “an embodiment” means that aparticular feature may be included in the practice of the invention.Similarly, it should be appreciated that in the foregoing description ofexemplary embodiments of the invention, various features of theinvention are sometimes grouped together in a single embodiment, figure,or description thereof for the purpose of streamlining the disclosureand aiding in the understanding of one or more of the various inventiveaspects. This method of disclosure, however, is not to be interpreted asreflecting an intention that the claimed invention requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the claimsfollowing the Detailed Description are hereby expressly incorporatedinto this Detailed Description, with each claim standing on its own as aseparate embodiment of this invention.

What is claimed is:
 1. A method comprising: receiving, at a subscriberstation, a pilot signal with a first set of spatial parameters as a widebeamwidth broadcast channel for use as a phase reference by a pluralityof different subscriber stations; transmitting, from the subscriberstation, a first user-specific traffic signal (hereafter first trafficsignal) with a second set of spatial parameters different from the firstset of spatial parameters as a narrow beamwidth traffic channel directedto another station; and transmitting, from the subscriber station, asecond user-specific diversity traffic signal (hereafter second trafficsignal) with a third set of spatial parameters different from the secondset of spatial parameters as a second narrow beamwidth traffic channeldirected to the same other station, the second traffic signal carryingthe same traffic as the first traffic signal.
 2. The method of claim 1,wherein transmitting the first traffic signal comprises transmitting thefirst traffic signal from a first antenna array of the subscriberstation, and wherein transmitting the second diversity traffic signalcomprises transmitting the second diversity traffic signal from a secondantenna array of the subscriber station.
 3. The method of claim 2,further comprising receiving a second pilot signal with the third set ofspatial parameters.
 4. The method of claim 2, wherein the first andsecond antenna arrays of the subscriber station are spatially separated.5. The method of claim 2, wherein the first and second antenna arrays ofthe subscriber station are differently polarized.
 6. The method of claim1, wherein transmitting the first and second traffic signals comprisestransmitting the first and second traffic signals each with a differentpolarization.
 7. The method of claim 1, wherein transmitting the firstand second traffic signals comprises transmitting the first and secondtraffic signals with spatial diversity.
 8. The method of claim 1,wherein transmitting the first and second traffic signals comprisestransmitting in accordance with a closed loop transmit diversity scheme.9. The method of claim 3, further comprising transmitting an indicationfrom the subscriber station of the relative phase of the received firstand second pilot signals for adjusting the relative phase of subsequentfirst and second traffic signals in accordance therewith.
 10. The methodof claim 1, wherein transmitting the first and second traffic signalscomprises transmitting in accordance with a space time block codingtransmit diversity scheme.
 11. The method of claim 1, further comprisingderiving transmission weights for the traffic signals by selectingtransmission weights that minimize the transmitted downlink power undera quality constraint of the delivered downlink traffic signal.
 12. Themethod of claim 1, wherein the subscriber station is located within atransmission sector, and wherein transmitting the pilot signal comprisestransmitting the pilot signal with a sector-wide beam.
 13. The method ofclaim 1, wherein the first and second traffic signals are the same. 14.The method of claim 1, wherein the pilot signal is a common pilotsignal.
 15. The method of claim 1, wherein transmitting the first andsecond traffic signals comprises transmitting the first and secondtraffic signals with narrower beam widths than the pilot signal.
 16. Amachine-readable non-transitory medium having stored thereon datarepresenting instructions which, when executed by a machine, cause themachine to perform operations comprising: receiving, at a subscriberstation, a pilot signal with a first set of spatial parameters as a widebeamwidth broadcast channel for use as a phase reference by a pluralityof different subscriber stations; transmitting, from the subscriberstation, a first user-specific traffic signal (hereafter first trafficsignal) with a second set of spatial parameters different from the firstset of spatial parameters as a narrow beamwidth traffic channel directedto another station; and transmitting, from the subscriber station, asecond user-specific diversity traffic signal (hereafter second trafficsignal) with a third set of spatial parameters different from the secondset of spatial parameters as a second narrow beamwidth traffic channeldirected to the same other station, the second traffic signal carryingthe same traffic as the first traffic signal.
 17. The medium of claim16, wherein the instructions for transmitting the first traffic signalcomprise instructions which, when executed by the machine, cause themachine to perform further operations comprising transmitting the firsttraffic signal from a first antenna array, and wherein the instructionsfor transmitting the second diversity traffic signal compriseinstructions which, when executed by the machine, cause the machine toperform further operations comprising transmitting the second diversitytraffic signal from a second antenna array.
 18. The medium of claim 17,further comprising instructions which, when executed by the machine,cause the machine to perform further operations comprising receiving asecond pilot signal at the subscriber station.
 19. The medium of claim16, further comprising instructions which, when executed by the machine,cause the machine to perform further operations comprising derivingtransmission weights for the traffic signals by selecting transmissionweights that minimize the transmitted uplink power under a qualityconstraint of the delivered uplink traffic signal.
 20. A subscriberstation comprising: a receive demodulator to receive and demodulate apilot signal with a first set of spatial parameters as a wide beamwidthbroadcast channel for use as a phase reference by a plurality ofdifferent subscriber stations; a transmit modulator to transmit andmodulate a data signal to form a first traffic signal to carry trafficto another terminal as a narrow beamwidth traffic channel directed toanother station, to apply a second different set of spatial parametersto the data signal for a second traffic signal directed to the otherterminal as a second narrow beamwidth traffic channel directed to thesame other station, the second traffic signal carrying the same trafficas the first traffic signal, and to apply a third set of spatialparameters different from the second set of spatial parameters to thedata signal for a third user-specific diversity traffic signal directedto the other terminal as a third narrow beamwidth traffic channeldirected to the same other station.
 21. The apparatus of claim 20,further comprising a first and a second antenna array, the first antennaarray to transmit the second traffic signal and the second antenna arrayto transmit the third diversity traffic signal and wherein the first andsecond antenna arrays are spatially separated.
 22. The apparatus ofclaim 21, wherein the first and second antenna arrays are differentlypolarized.
 23. The apparatus of claim 20, wherein the signal processoradjusts the relative phase of the second and second traffic signals inaccordance with the relative phase of a received first and second pilotsignals.
 24. The apparatus of claim 20, wherein the signal processorderives transmission weights for application to the transmit arrays byselecting transmission weights that minimize the transmitted power. 25.The apparatus of claim 20, wherein the pilot signal is a common pilotsignal.